1. Field of the Invention
The present invention relates to a vehicle periphery monitoring device which is mounted on a vehicle and monitors a vehicle periphery, and more particularly to a vehicle periphery monitoring device that detects, in a range extending from both sides of a subject vehicle to the rear, the presence/absence of a vehicle which is going to pass on an adjacent lane while coming close to the subject vehicle, or a vehicle which travels together, or the like, and judges whether the subject vehicle can change its lane or join in a main lane, or not, and also monitors the safety and the presence/absence of an obstacle such as a vehicle in the above range in a stationary manner.
2. Description of the Related Art
Up to now, there has been proposed that a radar device is mounted on a vehicle and widely used as a vehicle periphery monitoring device, or an inter-vehicle distance control device or the like.
The radar device mounted on the vehicle as the vehicle periphery monitoring device is so structured as to utilize a fender mirror or a fender portion of the vehicle, for example, as disclosed in Japanese Unexamined Patent Publication No. Sho 54-45040.
However, in the event of actually detecting a vehicle to be detected on an adjacent lane which is going to pass a subject vehicle, when the vehicle to be detected comes close to the subject vehicle at a relatively short distance, there is a case in which a distance of from the subject vehicle to the front most portion of the vehicle to be detected cannot be detected on the basis of the radial beam pattern characteristic of a radar antenna and a geometric condition. In other words, while the vehicle to be detected approaches the subject vehicle in a state where they travel together, a distance to, for example, a rear tire wheel portion which is on a side of the vehicle to be detected is detected. This is because if the vehicle to be detected travels substantially just laterally with respect to the subject vehicle, a detected distance value of a radar is farther than the actual distance to the front most portion of the vehicle which travels together. Therefore, in the above circumstance, the vehicle to be detected which is in a blind point region cannot be appropriately detected, and if the subject vehicle changes its lane, there is the possibility that the subject vehicle collides with another vehicle that travels together, resulting in a very dangerous state.
In addition, in order to judge the risk of the vehicle to be detected which travels at a relatively long distance, it is necessary to judge the risk at a distance as long as possible and at a high speed.
The present invention has been made in view of the above circumstances, and therefore has an object of the present invention to provide a vehicle periphery monitoring device which is capable of monitoring the risk of collision with an object in the periphery of a subject vehicle over an entire region of from a relatively short distance to a relatively long distance.
In order to achieve the above object, according to the present invention, there is provided a vehicle periphery monitoring device comprising: a transmitting circuit for generating a transmission wave; an antenna installed on the periphery or in the interior of a door mirror of a subject vehicle for radiating the transmission wave generated from the transmitting circuit as a formed beam having a directivity which propagates over a region expanding over an adjacent lane area from side portions of the subject vehicle toward the rear portion thereof; a receiving circuit for receiving a reflected wave from an object which is in the periphery of the subject vehicle through the antenna; arithmetically operating means for arithmetically operating a distance between the subject vehicle and the object on the basis of a period of time required since the transmission wave generated from the transmitting circuit is radiated from the antenna until the transmission wave is reflected by the object and received by the receiving circuit and arithmetically operating a relative velocity from Doppler frequency of a received electric wave or a value of differential from an arithmetically operated distance to judge the risk of collision with the object on the basis of those arithmetically operated results; and announcing means for announcing the judgement result by the arithmetically operating means to a driver in response to the risk.
Also, the arithmetically operating means, if the arithmetically operated distance is equal to or less than a given value, operates the announcing means to announce that the object is at a relatively short distance from the subject vehicle.
Further, it is characterized in that the arithmetically operating means, if the arithmetically operated distance exceeds the given value, judges a safe inter-vehicle distance according to the arithmetically operated relative velocity, and if the arithmetically operating means judges that an actual distance is shorter than the safe inter-vehicle distance, it operates the announcing means to announce that the actual distance to the object is shorter than the safe inter-vehicle distance.
Still further, it is characterized in that the arithmetically operating means varies a judgement level of the safe inter-vehicle distance according to a weather condition when judging the safe inter-vehicle distance.
Yet still further, it is characterized in that the antenna comprises a plane patch array antenna.
Yet still further, it is characterized in that the announcing means comprises an LED which is disposed on a lower portion of a mirror surface of the door mirror and announces the judgement result by the arithmetically operating means to the driver in response to the risk.
Yet still further, it is characterized in that the door mirror has a mirror surface on which reflective films of three primary colors which reflect the wavelengths of a visible light but transmits the electromagnetic waves of several G to 100 GHz are deposited.